The present invention relates to an improved method for producing a sealing member for a battery by integrally molding a gasket on the peripheral edge of a metal sealing plate.
There have been known batteries each having a metal container which accommodates a power generating element therein and a sealing member which seals the open end of the metal container. The sealing member has a metal sealing plate and a resin gasket. Those batteries use various electrolytes such as nonaqueous electrolytes, alkaline electrolytes and acid electrolytes. The sealing members had been produced by mounting a previously formed gasket on the sealing plate. To secure the adhesion between the sealing plate and the gasket thereby to achieve high electrolyte leakage resistance, an electrolyte-resistant sealing agent is interposed between them as necessary. Such process is indispensable especially in battery systems using alkaline electrolytes sinse the alkaline electrolyte itself exhibits a noticeable tendency to creep or a property of rising up along the metal surface.
As set forth, producing of sealing member required a step of molding a gasket and another step of integrally combining the gasket obtained and the sealing plate.
In order to simplify the process of producing such sealing members, there are proposed attempts of insert-molding a gasket on the peripheral edge of a sealing plate, for example, in Japanese Laid-Open Patent Publication No. Sho 50-91720.
The usual method for producing a sealing member by insert-molding the gasket onto a sealing plate is as follows. First, a sealing plate is provided between a female or concave mold of a molding apparatus having a concave face conforming to the upper surface of the sealing member to be obtained and a male or convex mold with a convex face conforming to the lower surface of the sealing member. The two molds are then clamped, followed by injecting a resin gasket material into a cavity formed on the peripheral edge of the sealing plate.
Usage of such ordinary molding apparatus for the above-mentioned insert-molding, however, inevitably brings about faulty moldings such as flowing out of resin onto unwanted areas of the sealing plate, detachment or dislocation of the sealing plate from the mold. These faults are caused by delicate differences or ununiformity in molding conditions including configuration of the sealing plate, molding temperature, molding pressure, mold clamping pressure, temperature of cooling water and molding cycle. Such faults also appears even when a lot of the resin gasket material is changed. The other problems encountered include sticking to the mold of the sealing agent applied to the sealing plate. Especially fatal is the resin flowing over to the inner surface of the sealing plate. Since the inner surface is in contact with the power generating element, the resin flowing over spoils conductivity of the battery.